Technology Workshop
How-To:  Air-Variable Capacitor From Scrap Aluminum


This lovely hand-made component, built as part of a crystal radio set Instructables user Jezan assembled for his son, started out as a sheet of 1.5 mm aluminum that looks like it may have come from the side of an old file cabinet. Jezan used minimal tools, laying out the part profiles by hand with a ruler and a compass improvised from a scrap of wood and a pair of nails. The parts are cut out with heavy scissors and re-flattened by pounding with a rubber mallet, then stacked and turned as a group on a hand drill to smooth and polish their edges. The mount was scavenged from a junk television and insulated with plastic cut from old jar lids, while the insulating bushing for the rotor is cut from a plastic pen cap.

30 thoughts on “How-To: Air-Variable Capacitor From Scrap Aluminum

    1. Should work just fine but be aware most (or many anyway) laptop drive platters and some desktop drives also, are made of glass with a magnetic coating.  I have destroyed many old drives by slapping them hard on a table top, the shock shatters the platters. Much faster than using a wipe utility to destroy data.

      You would also need to determine if the magnetic coating is electrically conductive, if not you would have to remove it where the segments are connected to each other.

  1. Nicely done. I’ve thought about something like this, but with copper cladded circuit boards. I wonder if oxidizing will help or hurt the capacitance and break over voltage?

  2. Nicely done. I’ve thought about something like this, but with copper cladded circuit boards. I wonder if oxidizing will help or hurt the capacitance and break over voltage?

  3. Nicely done. I’ve thought about something like this, but with copper cladded circuit boards. I wonder if oxidizing will help or hurt the capacitance and break over voltage?

  4. Nicely done. I’ve thought about something like this, but with copper cladded circuit boards. I wonder if oxidizing will help or hurt the capacitance and break over voltage?

  5. Excellent work!  Air-variable capacitors are getting really hard to find these days.  I don’t know that much about electronics, how would I measure the capacitance of a homemade variable capacitor? 

  6. Excellent work!  Air-variable capacitors are getting really hard to find these days.  I don’t know that much about electronics, how would I measure the capacitance of a homemade variable capacitor? 

  7. Excellent work!  Air-variable capacitors are getting really hard to find these days.  I don’t know that much about electronics, how would I measure the capacitance of a homemade variable capacitor? 

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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